Lemon grass (Cymbopogon citratur) is a tender perennial that is grown as an annual in many climates. It is used in Asian recipes, herbal teas and potpourri. Teas and the essential oil are used by herbalists for medicinal purposes. Lemon grass is also considered a mosquito repellent due to the presence of several aromatic oils. One variety -- Cymbopogon nardus -- is a source for citronella oil, an ingredient in a variety of insect-repellent products.
In a 2004 study presented at the California State Science Fair, a 25-percent lemon grass solution was tested against a commercial 15-percent Deet spray. The lemon grass brew was 51 per cent effective in repelling mosquitoes, compared to an effectiveness of 81 per cent for the Deet product. The study concluded that lemon grass showed promise as a partial replacement for Deet-based repellents. In a study conducted in 2010 at Maranatha Christian University, researchers compared lemon grass stem extract to citronella oil. Citronella oil proved more effective at repelling mosquitoes than the highest concentration of the lemon grass extract. Both studies reveal that while lemon grass does repel mosquitoes, it does not work as well as other products.
In the Garden
Some plant advertisements have implied that growing lemon grass plants in your yard or in a patio container will create a zone of protection from mosquitoes. Unfortunately, there is no evidence that the plants have that degree of effectiveness. To repel mosquitoes, the aromatic oils in lemon grass must be released by bruising or crushing the stalks. Having lemon grass specimens nearby as you work or relax outdoors does, however, offer the opportunity to grab a few stems to rub on your skin.
Although studies have shown that oils in the leaves and stems of lemon grass plants do possess some ability to repel mosquitoes, it's wise to proceed with caution. Before rubbing the leaves on every square inch of exposed skin, try it on a small patch on the inside of your arm to make sure you have no sensitivity to the oils. Watch for any skin irritation over the next day or two before considering lemon grass oil safe for you to use more liberally. You may need to reapply the lemon grass frequently to maintain an acceptable level of protection.
Jerry Butler, an entomologist at the University of Florida, created a natural insect repellent from a substance called geraniol, which was derived primarily from lemon grass, with the addition of several other herbs. It offers up to four hours of protection from mosquitoes, along with a variety of other insect pests. One version of the repellent was licensed to Naturale, Ltd. That company markets the substance under the trademarked name MosquitoSafe.